As the dimensions of semiconductor device features continue to shrink into the deep submicron range, it becomes increasingly more difficult to form the features with high dimensional accuracy. The minimum size of a feature depends upon the chemical and optical limits of a particular lithography system, notably the depth of focus of a particular tool. Therefore, it is of utmost importance to provide an extremely flat wafer or substrate surface during fabrication of integrated circuits as well as other electronic devices.
Conventional practices include planarizing a substrate surface to remove high topography by CMP, which typically involves introducing a chemical slurry during polishing to facilitate higher removal rates and selectivity between films on the substrate surface. Typically, CMP involves holding a substrate against a polishing pad under controlled pressure and rotational speed of the pad in the presence of the slurry or other fluid medium. The substrate is typically mounted in a carrier head and accommodated within a retaining device encircling the substrate to avoid slippage. The retaining device is typically configured in the shape of a ring and generally characterized as a retaining ring. A bottom view of a conventional retaining ring is schematically illustrated in FIG. 1 and comprises an inner annular surface 10 and an outer annular surface 11. A substrate is typically accommodated within and retained by inner annular surface 10.
A problem attendant upon conventional CMP is known as the “edge effect”, which is the tendency of the edge of the substrate to be polished at a rate different from the polishing rate at the center of the substrate. Thus, the edge effect typically results in either removing too much material from the substrate at the perimeter (overpolishing) and/or failing to remove sufficient material from the outer perimeter of the substrate (underpolishing) vis-à-vis the remainder of the substrate, resulting in an uneven edge polishing profile, thereby adversely impacting yield and/or reliability of devices fabricated on the substrate.
Accordingly, a need exists for retaining rings which eliminate or substantially reduce the edge effect encountered during conventional CMP. There exists a particular need for retaining rings which eliminate or substantially reduce the edge effect during CMP, can be utilized with a variety of substrates, and can be produced in a cost effective and efficient manner.